99 sportster speedo stuck at 55mph - 2004 Harley Davidson XL 883 Sportster

It can. Unplug it and see if it still stalls

The speedometer is not repairable. You simply replace it. There are places that specialize in "restorations" of speedometers but they mostly work on original equipment speedometers for collector's grade restorations and are VERY expensive. It's cheaper to simply replace the speedo. You may want to record the mileage on the bike and you'll probably have to note on the title that the mileage shown on the new speedo is not correct when you sell the bike.

Good Luck
Steve

speedo drive sensor may be faulty

had simular problem on my 2007. Speedo would die after bike was washed . Harley screwed with the bike several times replaced speedo nothing. Turns out to be connector on speedo water was getting into it and corroded it . Not enough grease put on connector when built.

could be a bad ground in the head light bucket or the jumper from frame to the triple tree

Harley had a whole bunch of bad speedos around that year. The replaced them free, but I don't think they will anymore. You might be stuck purchasing a new one.

This depends on whether it is an electronic speedo or a mechanical speedo.
The electric speedo has a sensor near the rear of the engine. Sometimes a very small piece of metal will get stuck on the end of the sensor and the speedo will stop working. Remove the bolt holding the sensor into the engine case and carefully pull the sensor out. Wipe it off and reinstall it. If the speedo still does not work, it's probably something in the speedo itself.

On a mechanical speedo, a cable from the front wheel drives the speedo. The cable or the speedo drive unit may be bad. To check the cable and drive, lift the bike off the ground, disconnect the cable from the rear of the speedo. Turn the front wheel and see if the cable is turning. If it is, it's probably alright. I'd still pull the cable out of it's housing and lubricate it with some grease. If the cable is turning, the cable and drive unit is alright. The speedo may be broken.

Press and hold the button until it flashes.

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